The present invention relates to a laser drive circuit and a recording apparatus using this laser drive circuit. More specifically, the present invention relates to an optical disc recording and reproducing apparatus for compact discs (CD-R (Recordable)/CD-RW (Read Write)), digital versatile discs (DVD-RAM (Random Access read write Memory)), magnet-optical (MO) discs, or other discs to which data can be written, as well as a laser drive circuit applied to this apparatus.
A known laser drive circuit applied to an apparatus of this kind is described, for example, in Japanese Patent Publication No. 8-3904 (hereafter referred to as a xe2x80x9cconventional examplexe2x80x9d).
FIG. 1 shows the laser drive circuit described in the conventional example. The laser drive circuit 100 comprises an operation amplifier (hereafter referred to as an xe2x80x9cOP amplifierxe2x80x9d) 101, an inverter circuit 102 having complementary output ends, PNP transistors 103, 104, 105, a resistor 106, a power terminal 110 to which a power supply Vcc is supplied, an input end 111 to which a setting voltage Vc is supplied for setting a drive current ILD, a terminal 112 to which a drive pulse signal CP for recording is supplied, and a terminal 113 having a semiconductor laser 114 connected thereto.
The setting voltage Vc supplied to the input end 111 is supplied to a non-inverted input end of the OP amplifier 101. Then, a base voltage of the PNP transistor 103 is controlled depending on the setting voltage Vc. A constant current Id output from a collector of the transistor 103 is supplied to an emitter of each of the PNP transistors 104, 105, which constitute a current switch.
In addition, the drive pulse signal CP supplied to the terminal 112 is supplied to the inverter circuit 102. Complementary output signals from the inverter circuit 102 are supplied to corresponding bases of the transistors 104 and 105. When the drive pulse signal CP is at a high level, an output signal from the inverter 102 turns on the transistor 105. This causes the constant current Id to be supplied to the semiconductor laser 114 through the terminal 113. On the other hand, when the drive pulse signal CP is at a low level, the output signal from the inverter circuit 102 turns on the transistor 104. This causes the constant current Id to flow to the ground.
In the laser drive circuit 100 in the above described conventional example, however, the constant current Id flows to the transistor 104 or 105 whether the drive pulse signal CP is at the high or low level. Normally, a drive current of 100 mA or higher is required for the semiconductor laser 114 during recording. The laser drive circuit 100 constantly consumes a current of 100 mA or higher. As a result, this circuit disadvantageously consumes a high current.
In particular, if the laser drive circuit 100 is located near the semiconductor laser 114, heat generated by the laser drive circuit 100 rises an operating temperature of the semiconductor laser 114. This results in a further increase in the drive current for the semiconductor laser 114, which is a serious problem.
On the other hand, optical disc recording and reproducing apparatuses are required to record data at a high speed. The laser drive circuit 100 in the conventional example, however, is constructed using the PNP transistors 103, 104, and 105. Accordingly, this circuit cannot essentially meet this requirement easily.
The object of the present invention is to provide a laser drive circuit that consumes less current and that can still operate at a high speed, as well as a recording apparatus using this laser drive circuit.
To attain the above object, according to a first aspect of the present invention, there is provided a laser drive circuit comprising a drive current source comprising a MOS transistor to generate a drive current depending on a setting current, a switch comprising a MOS transistor to supply the drive current supplied by the drive current source to a semiconductor laser, in response to a drive signal, and a stabilizing circuit connected to the drive current source to stabilize the drive current when the switch is turned on or off.
According to a second aspect of the present invention, there is provided a laser drive circuit comprising a drive current source comprising a MOS transistor to generate a drive current depending on a setting current, a control circuit configured to detect the setting current to control it depending on a setting voltage, and a switch comprising a MOS transistor to supply the drive current supplied by the drive current source to a semiconductor laser, in response to a drive signal.
According to a third aspect of the present invention, there is provided a recording apparatus comprising a drive circuit configured to generate a drive current for recording depending on a setting voltage for recording, and a semiconductor laser to which the drive current from the drive circuit is supplied, the drive circuit comprising a drive current source comprising a MOS transistor to generate the drive current depending on a setting current corresponding to the setting voltage, and a switch comprising a MOS transistor to supply the drive current supplied by the drive current source to the semiconductor laser, in response to a drive signal.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.